Graft copolymers

ABSTRACT

A process for the production of a graft copolymer comprises reacting an irradiated polymer in a reaction mixture comprising a first phase and a second phase. The first phase comprises a source of at least one non-water soluble monomer and the second phase comprises water and optionally, a water miscible organic solvent. The first and second phases are substantially immiscible and non-emusifiel. A high degree on monomer conversion is achieved.

[0001] This invention relates to an improved process for the preparationof graft copolymers using radiation induced grafting and to graftcopolymers made by such a process. The invention also relates to thegraft copolymers so produced as supports for catalytically activespecies.

[0002] The technology of modifying the properties of polymer materialshas interested chemists since the beginning of the nineteenth century.Early developments included the modification of rubber by isomerisationwith acid and by vulcanisation with sulphur. These developments inspiredchemists to more systematic work in applying organic chemistry pathwaysto modify the surface or bulk properties of polymers. To date a largenumber of synthetic polymers have been prepared and a number ofdifferent techniques have been developed to change or improve theproperties of polymers. The chemical modification of polymers has-becomea wide domain of polymer science and techniques such as coronadischarge, plasma and grafting are frequently employed for modification.

[0003] Generally, any reaction of classical organic chemistry can beapplied to modify or functionalise a polymer and reactions can becarried out in solution, in the melt or in the solid state. Cis-transisomerisations of polydienes, cyclisation of polyacrylonitrile, additionof maleic anhydride onto double bonds, and hydrolysis of polyvinylacetate to polyvinyl alcohol are examples of reactions that can becarried out in solution.

[0004] During the last twenty years, the modification of polymers usingradiation has become very important in polymer science and technology.The breakthrough in the industrial use of radiation took place in the1950's with the discovery of the crosslinking of polyethylene using highenergy radiation. Today the changes induced by radiation on theproperties of the most common polymers are well studied and documented.Applications such as radiation stabilisation and radiation inducedpolymerisation, crosslinking and grafting have gained central industrialimportance.

[0005] Irradiation leads to the formation of reactive species in thepolymers being irradiated. This can initiate chemical reactions. Theprocess of grafting, whereby side chains are attached to a host polymer,can be initiated by irradiation. The grafted polymer has distinctivelydifferent properties than those of the original polymer. If the sidechains comprise dissimilar monomer units to the host polymer, then thepolymer is a copolymer, whereas a homopolymer is formed when the monomerunits and the host polymer are similar. Among the different graftingtechniques (TV, plasma, chemical initiation) graft copolymerisationinduced by high energy radiation offers an attractive method ofpreparing new polymers for novel applications.

[0006] Most radiation grafting reactions utilise free radicals formedduring irradiation, and occur by a free radical mechanism. Ionicgrafting processes using ionising radiation are possible but arerestricted by the need to use high vacuum and extremely dry experimentalconditions.

[0007] Historically, radiation grafting has used low dose rate gammarays from ⁶⁰Co sources. During the past 10 years however, there has beenmuch interest in using high energy electrons from accelerators with highdose rates. High dose rates make radiation grafting processescommercially more attractive.

[0008] There are three common methods of radiation grafting: mutual,pre-irradiation and peroxide methods. In mutual (or direct) grafting,the polymer is irradiated in the presence of he monomer. This is asimple and effective method since the free radicals initiatepolymerisation immediately they are generated. The disadvantage of thismethod is however, that simultaneous graft copolymerisation andhomopolymerisation occurs upon irradiation. This reduces the yield ofthe desired copolymer. There are limited possibilities to alter theratio of graft copolymerisation versus homopolymerisation for example,by the addition of compounds such as Mohr's salt or FeCl₃, or by thecareful choice of the polymer-monomer system.

[0009] In a pre-irradiation process, the polymer is irradiated in aninert atmosphere and is subsequently immersed in a monomer solution. Theprocess requires additional steps in comparison to direct grafting, buthas the advantage that only a small amount of homopolymer is formed,mainly by a chain transfer process. The grafting process is initiated bytrapped radicals that are formed during irradiation and is controlled bythe diffusion of the monomer into the polymer. It can be facilitated bythe use of solvents that are able to swell the graft copolymer formed.

[0010] The peroxide process follows much the same process mechanism aspre-irradiation grafting. The main difference is that the polymer isirradiated in the presence of oxygen, thus forming peroxides andhydroperoxides that are stable and can be stored in the polymer for along period of time. Grafting is activated by cleavage of the peroxidesor the hydroperoxides by heat, UV-light or catalysis in a monomersolution.

[0011] One of the main concerns using radiation grafting on a productionscale is achieving a high conversion of the monomers used for grafting.A high conversion is not only is economically desirable, but alsodecreases the amount of waste material to be disposed of, and minimisesthe need for monomer recycling. It is clearly desirable to developradiation grafting processes with high monomer conversion.

[0012] WO 00/15679 describes a water based grafting process in whichmonomer units are grafted onto a cross linked polymer from a reactionmixture which comprises an emulsion of the monomer in water. Emulsifierssuch as alkyl sulphates and fatty acid esters are used in relativelyhigh proportions of up to 15 wt % of the reaction mixture in order toimprove wetting of the polymer and the stability of the emulsion.

[0013] U.S. Pat. No. 5,817,707 describes a process for making a graftcopolymer of a porous propylene polymer and a vinyl monomer. Thereaction mixture includes water and a surfactant. The function of thesurfactant is to produce an emulsion with water-immiscible monomers byforming stable micelles, as well as improving the solubility of themonomer in the aqueous phase. The surfactants may be an anionic,cationic or non-ionic.

[0014] A novel grafting process with significantly increased monomerconversion has been developed. The monomer solutions used in thepre-irradiation and peroxide grafting processes contain monomersimmiscible in water. The process of the invention is effective duringgrafting of such water immiscible monomers. If water is added to thesesolutions, two separate phases are formed. When irradiated polymerfibres are added to the monomer solutions, the fibres are forced intothe phase containing the monomers. This leads to a dramatic increase inmonomer conversion. Thorough agitation of the solution is alsobeneficial to high monomer conversion

[0015] Accordingly, the invention provides a process comprising reactingan irradiated polymer in a reaction mixture comprising a first phase anda second phase; wherein the first phase comprises a source of at leastone non-water soluble monomer; wherein the second phase comprises water;and wherein the first and second phases are substantially immiscible andnon-emulsified.

[0016] Preferably, the second phase further comprises a water miscibleorganic solvent.

[0017] The invention further provides grafted copolymers made by such aprocess.

[0018] Suitable polymers include polyolefins and fluorinatedpolyolefins, particularly polyethylene, but other polymers may also beconsidered, and the invention applied advantageously to such polymers.

[0019] The polymer may be in any form, including especially beads andfibres, although there may be technical interest in other forms such asfilms.

[0020] The monomers in the reaction mixture may comprise any non-watersoluble monomers however preferably, the monomers are selected from thegroup of styrene and derivatives, vinyl benzyl derivatives such as vinylbenzyl chloride, styryl diphenyl phosphine, vinyl benzyl boronic acid,vinyl benzyl aldehyde and derivatives, α-methyl styrene, α-methylstyrene derivatives such as m-isopropyl-α,α-dimethyl benzyl isocyanate,vinyl acetate, vinyl pyridine and vinyl sulphonic acid. If the reactionmixture comprises more than one type of monomer, the resulting polymerwill have varied monomer units.

[0021] Suitably, water comprises from 5 to 80% by weight of the reactionmixture, preferably between 20 and 50% by weight.

[0022] Suitably, the water miscible organic solvent comprises an alcoholor another water miscible solvent and preferably, the water miscibleorganic solvent comprises ethanol.

[0023] The irradiation step may be carried out in an inert atmosphere.In this case the process is a pre-irradiation grafting process. Theatmosphere is suitably nitrogen.

[0024] If irradiation is carried out in an inert atmosphere, it isdesirable to remove in advance any dissolved oxygen from the reactionmixture before the polymer is added. This may be achieved by forexample, purging the mixture with nitrogen.

[0025] In the first embodiment, after the irradiation step, theirradiated polymer is immersed in the reaction mixture. Preferably,immersion is substantially immediately or shortly after irradiation,although a longer interval between irradiation and immersion may stillbe effective.

[0026] In a further embodiment, the irradiation step may be carried outin the presence of oxygen. In this case, the process is a peroxidegrafting process and suitably, further comprises a cleavage step afterthe immersion of the irradiated polymer in the reaction mixture. Theperoxides or hydroperoxides are cleaved and grafting is initiated by forexample, heat, by the application of UV light, or by catalysis.

[0027] Irradiation of the polymer can be carried out with any suitableform of ionising radiation, suitably accelerated electrons. Theradiation dose delivered is dependent on the polymer and thespecifications of the final product. Typically, the dose is in the rangeof 50 kGy to 300 kGy.

[0028] In the pre-irradiation embodiment of the process it can be usefulto add small amounts of an initiator such as benzoyl peroxide. It may benecessary to heat the solution to cleave the initiators.

[0029] It may be beneficial to add cross-linkers. Di- or tri-functionalmonomers can cross-link the graft chains thus altering thecharacteristics of the final product. Suitable cross-linkers includedivinyl benzene, di- or tri(meth)acrylate and di- ortri(meth)acrylamide.

[0030] The polymer may be irradiated and then suspended in the reactionmixture and permitted to react with the monomer. Alternatively, thepolymer may be suspended in the second phase and irradiated. The monomer(first phase) may then be added to form the reaction mixture, or thesecond phase containing the irradiated polymer may be added to the firstphase.

[0031] The reaction, of monomer with irradiated polymer may be carriedout at ambient temperature, or at elevated temperature, e.g. up to 100°C. under ambient pressure.

[0032] After completion of the reaction, separation of the polymer issuitably achieved, by filtering. Washing is preferably carried out toremove any residual monomer or homopolymer formed during the reaction. Asuitable washing procedure comprises firstly washing with ethanol, andthen with dichloroethane or acidified water.

[0033] The grafting process according to the invention has manyadvantages. The conversion of the monomers added to the graft solutionis close to 100%, and thus expensive recovery and recycling of themonomers can be reduced. Accordingly, the process is moreenvironmentally friendly since the formation of waste material isminimised. The process is also more easily controlled allowing variationfrom batch to batch to be avoided, leading to improved product quality.

[0034] By using the graft process according to the invention it is easyto prepare graft copolymers with a pre-determined capacity of functionalgroups. Monomer conversion is significantly higher than that which canbe achieved using conventional grafting techniques, giving a higherdensity of graft chains. Preferably, monomer conversion is greater than60%, more preferably greater then 70%, and in some cases greater than90%.

[0035] The graft copolymers can be further modified using conventionalorganic chemical reactions. For example, aminations, lithiations,chlorinations, brominations, esterifications, etherfications, Suzuki andHeck couplings etc., can be used to provide chemically modified graftcopolymers.

[0036] The graft copolymers or chemically modified graft copolymers canbe loaded with one or more metals or metallic species to formcatalytically active materials. This may be achieved by any suitablemethod for example, by immersing the graft copolymers in a solution ofthe metal or metals of interest. Examples of suitable metals are knownin the art and include the platinum group metals, such as Pt, Pd, Ru,Rh, Ir and Os, and transition metals, such as Fe and Ni. The performanceof such catalysts can be tailored by changing the metal content, theratio of different metals and the chemical functionality of the graftpolymer. The catalysts so formed may be used for any suitable catalyticprocess or reaction for example, Suzuki-Miyaura couplings and Heckreactions. Catalyst supports comprising graft copolymers produced usingthe process described herein form a further aspect of the presentinvention.

[0037] The skilled person will be able to see many ways of producingimproved graft copolymers and chemically modified graft copolymers inaccordance with the invention.

[0038] It is believed that the invention provides novel graft copolymersuseful in many fields but especially in catalysis and ion-exchange torecover or refine metals. Tests are ongoing to establish the definitionand/or analysis of such novel copolymers. It is the intention of theApplicants to claim all novel processes, products and products derivedfrom the present invention.

[0039] The invention will now be illustrated by way of example only.

EXAMPLE 1

[0040] 350 g of cut polyethylene fibres (0.7 Dtex) were irradiated in aninert atmosphere to a total dose of 150 kGy using an electronaccelerator operating at an acceleration voltage of 175 kV and beamcurrent of 5 mA. The irradiated fibres were immediately immersed in areaction mixture containing 203 g 4-vinyl pyridine, 412 g ethanol and612 g water. The reaction mixture was purged with nitrogen beforeinitiating the reaction and the grafting reaction was allowed tocontinue to completion, which took approximately 6 hours.

[0041] The resulting fibres were filtered from the reaction mixture andwashed with ethanol and finally with dichloroethane or with an acidifiedwater solution. The weight gain of the recovered fibres was determinedand the conversion of the monomer was calculated to be 100%.

EXAMPLE 2

[0042] Example 1 was repeated with a reaction mixture containing 200 gstyrene, 600 g ethanol and 400 g water. The conversion of the monomerwas calculated to be 82%.

EXAMPLE 3

[0043] Example 1 was repeated with a reaction mixture containing 203 gstyrene, 400 g ethanol and 600 g water. 3 g of divinyl benzene and 3 gof a 25 wt % solution of dibenzoyl peroxide were also added to thereaction mixture. The reaction took approximately 2 hours to reachcompletion. After the 2 hours the solution temperature was raised to 80°C. and maintained there for 4 hours. The conversion of the monomer wascalculated to be 91.7%.

EXAMPLE 4

[0044] Example 1 was repeated with 223 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing 153 g styrene, 23 g vinyl benzylchloride, 588 g ethanol and 203 g water. The conversion of the monomerwas calculated to be 80%.

EXAMPLE 5

[0045] Example 1 was repeated with 134 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing 116 g styrene, 80 g vinyl benzylchloride, 166 g ethanol and 308 g water. 1 g of divinyl benzene and 1 gof a 25 wt % solution of dibenzoyl peroxide were also added to thereaction mixture. The conversion of the monomer was calculated to be99.5%.

EXAMPLE 6

[0046] Example 1 was repeated with 10 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing 20 g styrene, 5 g styryldiphenyl phosphine, 50 g ethanol and 20 g water. 0.15 g of divinylbenzene and 0.135 g of a 25 wt % solution of dibenzoyl peroxide werealso added to the reaction mixture. After the reaction was complete thetemperature was raised to 80° C. for 1 hour. The conversion of themonomer was calculated to be 76%. Elemental analysis of the copolymergave a phosphorus content of 1.79%, indicating the extent of grafting ofthe styryl diphenyl phosphine.

EXAMPLE 7

[0047] Example 1 was repeated with 10 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing 20 g styrene, 2 g styryldiphenyl phosphine, 50 g ethanol and 20 g water. 0.02 g of divinylbenzene and 0.2 g of a 25 wt-% solution of dibenzoyl peroxide were alsoadded to the reaction mixture. After the reaction was complete thetemperature was raised to 80° C. for 1 hour. The conversion of themonomers was calculated to be 91%. Elemental analysis gave a phosphoruscontent of 0.76%.

EXAMPLE 8

[0048] Example 1 was repeated with 10 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing 20 g styrene, 0.5 g vinyl phenylboronic acid, 50 g ethanol and 20 g water. 0.03 g of divinyl benzene and0.2 g of a 25 wt-% solution of dibenzoyl peroxide were also added to thereaction mixture. After the reaction was complete the temperature wasraised to 80° C. for 1 hour. The conversion of the monomers wascalculated to be 93%.

EXAMPLE 9

[0049] 9a Preparation of Palladium Catalyst

[0050] Polyethylene fibres modified with styrene/styryldiphenylphosphineco-polymer prepared according to the invention (60 g batch) were stirredin dichloromethane (480 ml). Palladium acetate (9.05 g, 1.25 equivalentsrelative to P in the polymer) was added. The mixture was stirred for twohours and the polymer fibres were then collected by filtration. Theywere washed thoroughly with dichloromethane and dried in air, then invacuo.

[0051] Yield: 67.9 g

[0052] 9b Suzuki-Miyaura Coupling using Catalyst Prepared as above in 9a

[0053] The Pd catalyst (20 mg) was mixed with 4-bromoacetophenone (1M intoluene, 1.65 ml) phenylboronic acid (0.305 g) and potassium carbonate(0.449 g) in toluene (3.35 ml). The mixture was stirred and heated to70° C. under nitrogen. After two hours the solution was allowed to coolto room temperature and was filtered. Analysis of the filtrate by gaschromatography indicated complete conversion of 4-bromoacetophenone to4-acetylbiphenyl.

[0054] 9c Heck Reaction using Pd Catalyst Prepared as above in 9a

[0055] The Pd catalyst (20 mg) was mixed with 4-bromoacetophenone (0.71g) n-butyl acrylate (0.64 g) and sodium acetate (0.32 g) inN,N-dimethylacetamide (5 ml). The mixture was stirred and heated to 100°C. for 24 hours under nitrogen. The solution was allowed to cool and wasfiltered. Analysis of the filtrate by gas chromatography indicated 97%conversion of 4-bromoacetophenone to 4-acetyl-n-butylcinnamate.

COMPARATIVE EXAMPLE 1

[0056] Example 1 was repeated with 250 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing only 1040 g styrene. No waterwas present in the reaction mixture. The conversion of the monomer wascalculated to be 33%.

COMPARATIVE EXAMPLE 2

[0057] Example 1 was repeated with 100 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing only 460 g vinyl benzyl chlorideand 200 g ethanol. No water was present in the reaction mixture. Theconversion of the monomer was calculated to be 25%.

COMPARATIVE EXAMPLE 3

[0058] Example 1 was repeated with 115 g of cut polyethylene fibres (0.7Dtex) and a reaction mixture containing only 427 g 4-vinyl pyridine and210 g ethanol. No water was present in the reaction mixture. Theconversion of the monomer was calculated to be 18%.

1. A process for the production of a graft copolymer, the processcomprising reacting an irradiated polymer in a reaction mixturecomprising a first phase and a second phase; wherein the first phasecomprises a source of at least one non-water soluble monomer; whereinthe second phase comprises water; and wherein the first and secondphases are substantially immiscible and non-emulsified.
 2. A processaccording to claim 1, wherein the second phase further comprises a waterto miscible organic solvent.
 3. A process according to claim 1 or claim2, wherein the polymer is a polyolefin or a fluorinated polyolefin.
 4. Aprocess according to any preceding claim, wherein the at least onenon-water soluble monomer is chosen from the group comprising; styreneand derivatives, vinyl benzyl derivatives, vinyl benzyl chloride, styryldiphenyl phosphine, vinyl benzyl boronic acid, vinyl benzyl aldehyde andderivatives, α-methyl styrene, α-methyl styrene derivatives,m-isopropyl-α,α-dimethyl benzyl isocyanate, vinyl acetate, vinylpyridine and vinyl sulphonic acid.
 5. A process according to anypreceding claim, wherein water comprises from 5 to 80% by weight of thereaction mixture.
 6. A process according to claim 5, wherein watercomprises from 20 to 50% by weight of the reaction mixture.
 7. A processaccording to any of claims 2 to 6, wherein the water miscible organicsolvent comprises an alcohol.
 8. A process according to claim 7, whereinthe water miscible organic solvent comprises ethanol.
 9. A processaccording to any preceding claim, wherein the polymer is irradiated inan inert atmosphere.
 10. A process according to any of claims 1 to 8,wherein the polymer is irradiated in the presence of oxygen.
 11. Aprocess according to any preceding claim, wherein the reaction mixturefurther comprises an initiator.
 12. A process according to claim 11,wherein the initiator comprises benzoyl peroxide.
 13. A processaccording to any preceding claim, wherein the reaction mixture furthercomprises a cross-linker.
 14. A process according to claim 13, whereinthe cross-linker comprises divinyl benzene, di- or tri-(meth) acrylate,or di- or tri-(meth) acrylamide.
 15. A graft copolymer prepared by aprocess according to any of claims 1 to
 14. 16. A graft copolymeraccording to claim 14, wherein monomer conversion is greater than 60%.17. A catalyst support material comprising a graft copolymer accordingto claim 15 or claim 16.